Workshop on Nonstationarity, Hydrologic Frequency Analysis,

and Water Management

Julie Kiang, U.S. Geological Survey

Rolf Olsen, U.S. Army Corps of Engineers

What is stationarity?

• The assumption behind traditional hydrologic frequency analysis is that climate is stationary.

• Stationarity means that the statistical properties of hydrologic variables in future time periods will be similar to past time periods.

“Stationarity is Dead”

• “Stationarity is a foundational concept that permeates training and practice in water-resource engineering.”

• “Climate change undermines a basic assumption that historically has facilitated management of water supplies, demands, and risks.”

Alternatives to Stationarity Assumption

• Although there have been academic articles criticizing the assumption of stationarity, it is not apparent what, if any, alternative methods should be used as a replacement.

Workshop Objectives

• Discuss whether there is a need for new ways to model nonstationary processes for hydrologic frequency analysis and if current approaches are not working.

• Present a range of potential alternatives for dealing with non-stationarity in hydrology both in the near term, as well as for the next generation of analytical tools that could be developed.

Workshop Objectives (continued)

• Compile workshop proceedings based on invited papers and minutes from the meeting.

• Initiate mechanisms for a continuing dialog between water managers and scientists on methods to deal with climate uncertainty.

• Formulate an ‘Action Plan’ for next steps to develop practical guidance for water managers to deal with climate uncertainty.

Organizing Agencies

• International Center for Integrated Water Resources Management

• U.S. Army Corps of Engineers

• U.S. Geological Survey

• U.S. Bureau of Reclamation

• National Oceanic and Atmospheric Administration

• Environmental Protection Agency

• Colorado State University

Some Other Agency Attendees

• Federal Emergency Management Agency

• Federal Highway Administration

• Natural Resources Conservation Service

• U.S. Forest Service

• U.S. Navy

• Denver Water

• Western Governors Association

• Manitoba Hydro

International Participants• United Kingdom, Walker Institute, University of Reading• Poland, Research Centre for Agricultural and Forest

Environment, Polish Academy of Sciences• Japan, International Center for Water Hazards and Risk

Management • United Kingdom, University of Exeter, London School of

Economics • Canada, Institut national de la recherche scientifique

(INRS)• Greece, National Technical University of Athens

Some Ideas from Workshop – Stationarity

• Nonstationarity is here and always was – Get over it!

• Stationarity was never alive.

• The problem is our perception that climate should be stable.

Some Ideas from Workshop – Statistical Methods

• Federal government should provide adequate resources to keep hydrologic data, information, and methods up-to-date – precipitation frequency estimates, probable maximum precipitation, methods for flood frequency estimation (Bulletin 17B).

• It may be time to give Bulletin 17B a decent burial and move on.

Some Ideas from Workshop – Global Climate Models

• Models have deficiencies – they don’t contain some physical processes and other processes are poorly represented.

• Downscaling helps people do the wrong things more precisely.

• We are riding a bicycle backwards if we look only at the historical record.

• GCM based projections give us some insights, warts and all.

Some Ideas from Workshop – Uncertainty

• There are inherent irreducible uncertainties in climate science.

• It is a misleading idea to constrain the uncertainty in climate models.

• When using uncertain information, we must manage the residual risk.

Some Ideas from Workshop – Water Management

• Climate change challenges analytical techniques and decision making.

• We are interested in making better decisions, not in better predictions.

• We need to shift from a static design paradigm to dynamic management.

• We may need a new Harvard Water Program (an effort to improve decision making with uncertainty).

Some Ideas from Workshop – Science

• Hydrologic community needs to better use non-traditional data.

• Scientific community needs to better understand ongoing hydrologic change.

• We need a better understanding of the mechanism of extreme events.

International Next Steps

• U.N. Secretary General’s Advisory Board on Water and Sanitation (UNSGAB)/ High-Level Expert Panel on Water and Disaster (HLEP)

• LTG Robert Van Antwerp (Commanding General, U.S. Army Corps of Engineers) is member of HLEP

• Published Water and Disaster, a report of action plans to reduce impact of water-related disasters.

International Next Steps

• USACE has agreed to lead Task 29 action:

“National and international hydrological institutes must take the initiative to identify underlying analytical and data requirements to meet climate changes that are likely to be highly uncertain and so as to support structural and non-structural measures for disaster risk deduction.”

Next Steps

• Proceedings including abstracts, presentations, papers – it will be an online resource for issues of nonstationarity and water management.

• Feature Collection of invited papers in Journal of American Water Resources Association (JAWRA).

Next Steps

• Federal agencies “must take the initiative to identify underlying analytical and data requirements to meet climate changes that are likely to be highly uncertain.”

• Federal agencies should review decision making methods for uncertain, dynamic conditions.

• What is proper working group to develop practical guidance for water managers to deal with climate uncertainty?

Questions?